A variety of actuators are in practical use for producing a driving force by flowing an electric current into an inductive element such as a solenoid and varying the electromagnetic state. In an internal combustion engine, for example, such an actuator is mounted on an injector that injects fuel, and drives the valve of the injector.
A drive apparatus for driving the electromagnetic load having the inductive element includes a capacitor as a capacitive element in addition to a battery which is a DC low voltage power source. In this apparatus, the energy accumulated in the inductive element due to the supply of electric power is recovered by the capacitive element by generating a counter electromotive force at the time when the operation of the electromagnetic load is stopped (EP 0548 915A1, JP 2598595).
In this apparatus, the electric power is supplied to the inductive element from the capacitive element until the voltage across the terminals of the capacitive element becomes equal to the voltage across the terminals of the low voltage power source. Thereafter, the electric power is supplied from the low voltage power source.
The actuator utilizing the inductive element is highly appreciated for its response characteristics when the current supplied to the inductive element rises quickly. The rise of current supplied to the inductive element varies nearly in proportion to the voltage applied to the inductive element.
When it is desired to increase the voltage applied to the inductive element, the capacitance of the capacitive element may be decreased to elevate the voltage across the terminals of the capacitive element after the energy is recovered. From the breakdown voltage of the capacitive element, however, it is not allowed to increase the voltage across the terminals of the capacitive element.
Further, as the power source is shifted to the low voltage power source, there is almost no change in the electric current that flows into the inductive element. Namely, the energy accumulated in the inductive element does not increase so much. All energy that had been held before the operation is not recovered by the capacitive element. Therefore, the loss of energy must be replenished until the next operation. However, the energy cannot be sufficiently replenished when the interval is short until the next operation of the actuator. For example, when the same injector is consecutively operated within short periods of time like the multi-step injection of the internal combustion engine, the response drops toward the subsequent operations.